Deck on a Slope: Set Pier and Beam Heights in ArchiMaster 3D

A sloped backyard stops more deck projects than weather or budget. In ArchiMaster 3D, the solution is not guessing post lengths; it is modeling the terrain and then setting each pier and beam to a measured elevation above a shared datum. This walkthrough covers exactly that workflow: build the site first, place footings at true ground height, then set beam elevations so every joist lands level. Late August 2026 is the right time to test this because the same model you build now can drive a fall permit set and material list.

• A sloped deck in ArchiMaster 3D starts with the lot's terrain model, not the deck tools; accurate elevation data drives every pier height.
• Use a reference plane or terrain height at each post location to set pier top elevations minus the beam and joist assembly thickness.
• For a walkable deck on a slope, keep the finished deck surface within one step, about 7 inches, of the adjacent interior floor or stair landing.
• Model each footing as an object tied to the terrain, then check the beam top against a uniform datum to avoid stepped or twisted framing.
• ArchiMaster 3D's one engine across editions lets you reuse the same sloped terrain model for deck, landscape, and retaining wall planning.

Model the Sloped Terrain Before You Place a Single Post

Most deck tutorials start with the decking rectangle. On a slope, that is a mistake. A deck's piers sit on actual ground, not on a flat 0-inch plane, so the terrain model is the first thing you build. In ArchiMaster 3D, open the landscape or terrain tools and draw the lot's approximate contour lines. If you have a survey PDF, import it as an underlay and trace the elevation markers. Then assign each contour its true elevation. A common backyard slope of 1 foot of rise over 10 feet of run, a 10 percent grade, changes pier heights by 14.4 inches across a 12-foot deck. That is the difference between a level deck and a trip hazard.

Use a reference plane for the finished deck height

Once the terrain exists, set a reference plane at the proposed finished deck elevation. This plane is not a physical object; it is a measuring tool. In ArchiMaster 3D, add a horizontal plane at the elevation where the deck boards should sit, aligned with the house ledger or a chosen stair landing. Then measure down from that plane to the terrain surface at every post location. The difference minus the beam and joist assembly thickness is the cut length of each post. Doing this before placing posts prevents the common error of setting post tops all at the same absolute height, which makes the beam tilt on a slope.

Set Pier Elevations from a Datum, Not the Ground

The single most useful habit when modeling a sloped deck is to stop reading height from the ground under each post. Ground height varies, so it gives you a different zero at every pier. Instead, set a shared datum, often the top of the house ledger or the top of a stair landing, and give every pier a height measured down from that datum. In ArchiMaster 3D, select each footing or pier object and type its top elevation in the properties panel. For a typical 2x8 joist plus 5/4 decking assembly, subtract about 8.75 inches from the finished deck height to find the beam top. Then subtract the beam depth, usually 7.25 inches for a 2x8 or 9.25 inches for a 2x10, to find the pier top.

Model the footing below grade

The footing itself must extend below local frost depth. In many U.S. climates that means 12-inch diameter concrete tubes set 36 to 48 inches below grade, with the pier top above grade by whatever the slope requires. In ArchiMaster 3D, place a cylinder for the concrete tube and a shorter post object above it. Set the tube's bottom below the terrain surface at each location, then set the post top to the pier elevation you calculated. This gives a buildable detail: the tube length varies with the slope, while the post above grade stays a manageable 12 to 18 inches on the uphill side and may reach 3 to 4 feet on the downhill side.

“A deck on a slope fails one post at a time, and the fix is a shared datum, not a longer post.”, ArchiMaster 3D Journal

Stack the Beam and Joist Heights Above Each Pier

After piers are placed, model the beam as a continuous horizontal member running across the posts. On a sloped deck, the beam is not sloped; the posts are different lengths. Set the beam's elevation to the beam top you calculated, then run joists from the ledger outward to the beam. In ArchiMaster 3D, the joist tool uses the beam and ledger elevations to keep the top of the framing flat. Verify by switching to a front or side orthographic view and zooming in on the beam-to-post connections. If you see a gap or a post poking through the beam, the pier top is off by the exact difference between your datum and the terrain. Adjust one number to fix it, not the whole frame.

Check the ledger, stair landing, and knee bracing

The ledger on the house side is your elevation anchor. Set the ledger top to match the interior finished floor if you want a flush walk-out, or drop it 7 to 7.5 inches for a step down. On a slope, the downhill edge often sits several feet above grade. That exposed area is where you model knee bracing or a skirt board. In ArchiMaster 3D, add diagonal braces from the posts to the beam or rim joist, then check that no brace blocks a window, a vent, or a future stair run. If you are planning a pergola over that same deck, the post and beam logic is almost identical; see Attached vs Freestanding Pergola: Compare in ArchiMaster 3D.

Check Stairs, Guardrail Clearance, and the 36-Inch Rule

A sloped deck almost always includes stairs, which is where elevation errors surface. In ArchiMaster 3D, drop a stair object from the low corner of the deck to the grade below. The stair tool will report the total rise and the number of treads. If the grade at the landing is uneven, you may need a small landing pad or a second short run. Keep the rise per step between 6 and 7.75 inches for comfort; outside that range, adjust the deck height or the landing location. Then check the guardrail. Most U.S. residential codes require a 36-inch rail height for residential decks and 42 inches for higher decks, with balusters spaced no more than 4 inches apart. Model the rail along the sloped side and verify the bottom rail does not create a toe catch.

• Finished deck surface at the house: flush or one 7-inch step down from the interior floor.
• Beam top: finished deck height minus joist and decking depth, about 8.75 inches.
• Pier top: beam top minus beam depth, typically 7.25 to 9.25 inches.
• Bottom of concrete tube: below local frost depth, commonly 36 to 48 inches.
• Guardrail height: 36 inches for residential decks, 42 inches for higher decks.

Export the Pier Schedule and Cut List Before Fall Remodeling

The value of modeling the slope accurately is that ArchiMaster 3D can turn the model into the numbers your contractor needs. Before you schedule fall work, generate a materials list and pier schedule. Sort posts from shortest to longest and label each one with its location and cut length. On a 20-foot-wide deck with a 12 percent side slope, the downhill post can be more than 24 inches longer than the uphill post, and a manual guess will be off. A sorted schedule eliminates that error. If you are working with a contractor, export a 2D elevation of the beam and posts; it is often the single clearest drawing for a permit reviewer.